With precision investment castings, the first step involves the engineering and production of a mould also known as a wax tool. Moulds are made from aluminum or steel. This mould is developed in-house by hoohi engineers and serves as a negative of the final casting. It is important that the mould is made accurately, so that the required tolerances and surface roughness can be achieved. Depending on the size of the series, the mould is installed either onto a manual or automated press.

Step 2: Wax model spraying & Tree building

The mould is filled with liquid wax. After the wax has been cooled down, ejectors in the mould push the wax model out. A wax model has now been sprayed which is identical to the final casting. These wax models are glued onto a so-called wax tree with a casting funnel on top, into which steel is poured in a later stage of the process

Step 3: Rinsing the wax trees

After the wax models have been glued onto a wax tree, they are rinsed. Any possible contaminations on the surface are removed to ensure a successful attachment of the ceramic onto the wax tree.

Step 4: Building ceramic layers

After rinsing the wax tree, the tree is given a fireproof ceramic shell. This shell is constructed after repeatedly submerging the tree (up to 7 or 9 times) in a slurry and sprinkling it with ceramic sand. The ceramic layers are then hardened in a drying chamber where they are exposed to air.

Step 5: Autoclave

After the layers have been formed and dried, the wax is melted out of the ceramic tree by using steam (120°C) in an autoclave. This is why it is called “lost wax casting”. The majority of the molten wax can be regenerated and is reusable.

Step 6: Sintering

The ceramic tree is then baked (stoked) at temperatures of around 1100°C and reaches its final strength through the sintering process. Any wax remains are burned out during this process.

Step 7: Casting

The desired steel alloy is melted in a large furnace and brought to cast temperatures. The ceramic tree is, at the same time, heated in an oven to prevent thermal shocks during the pouring process. After the tree has been heated, it is removed from the oven by a robotic arm and filled up with a steel alloy by use of counter gravity. When the trees have been poured, they are placed on a cooling conveyor where they are cooled down. (with nitrogen).

Step 8: Ceramic removal

The trees are then removed from their ceramic shell by using a fully-automatic hammer to break the shell. This removes the majority of the ceramic. The next step is to cut the products from the trees by sawing or vibrating. The steel leftovers will be sorted based on alloy and can be melted again during the next casting session

Step 9: Blasting

The Finishing Department removes the last pieces of ceramic by means of steel, sand and/or water blasting.

Step 10: Grinding

The ingate which remained after the sawing process, is grinded from the casting. To grind the product properly, a grinding fixture is often applied.

Step 11: Visual inspection

The Quality Department checks all products visually for possible casting failures. This check takes place according to a quality standard sheet to ensure that all possible surface failures are corrected properly. Thanks to this procedure, you can be assured that hoohi only delivers high quality castings.

Step 12: Machining

hoohi has the capabilities to machine castings in house, such as drilling holes, tapping threads and turning & milling activities. This enables hoohi to deliver a completely machined component that is ready-to-install.

Step 13: Heat and- or surface treatment

Some alloys require heat treatment to achieve a certain hardness, tensile strength or elongation according to 2D drawing specifications. The standard heat treatments are performed in-house, the complex treatments are outsourced. hoohi also has the know-how to perform a surface treatment for a casting. Surface treatments involve the coating process of a steel surface, to enhance the looks of the surface or protect it against external influences such as corrosion (rust) and natural wear (damage).

Step 14: Final inspection

The final step in this process is another visual check and when necessary composing a measurement report and material analysis. After the final inspection, the products are ready for shipment to another satisfied Hoohi customer.